Hydrogen is an important element for many chemical processes and is used in many technical methods. Hydrogen is required, for instance, as fuel for the generation of electric energy in fuel cells on board motor vehicles. However, because of the hazards of storing hydrogen, hydrogen is typically not stored on motor vehicles. Instead, apparatuses and processes have been developed to generate hydrogen on board motor vehicles from gasoline or diesel fuel in order to form a gas stream that contains hydrogen.
In one method, for instance, steam is added to the fuel and this mixture is converted in what is referred to as a steam reforming process into hydrogen and carbon monoxide. The hydrogen is used as fuel for a PEM fuel cell. This steam reforming process is endothermic and requires an additional burner for heating the reforming reactor to the required reaction temperature of from about 700 to 800° C.
Alternatively, the reforming process can be conducted auto thermally by adding a certain amount of oxygen to the mixture of steam and fuel such that first heat is generated by catalytic partial oxidation (CPO) of the fuel and then causing steam reforming to commence. According to this process, the reformate comprises about 30 to 40% by volume of hydrogen and additionally 10 to 15% by volume of carbon monoxide, which must be reduced to below 50 ppm by volume by means of subsequent purification steps (high and low temperature shift steps; HTS and LTS; preferential oxidation PROX) in order to avoid contamination of the PEM fuel cell.
A process for auto thermal steam reforming of hydrocarbons is described in US 2002/0009408 A1. This process requires heating of the reaction mixture to a pre-heating temperature and then feeding the reaction mixture to a catalytic reactor for performing the auto thermal steam reforming. In total, conventional auto thermal steam reforming is performed in a bulky and elaborate apparatus.
Since hydrogen or a gas enriched in hydrogen may be used in a vehicle for various purposes, there is a need to develop a more compact apparatus and efficient process for the generation of hydrogen on board a vehicle. The present invention provides one solution to this problem